1. Field of the Invention
The present invention relates to a structure for managing an umbilical member of a welding torch in an arc welding robot.
2. Description of the Related Art
In a conventional arc welding robot, a configuration has been known in which a welding torch is attached to the distal end of a forearm of the robot, and a wire feeding device is provided on the forearm so as to feed a welding wire, through a torch cable, to the welding torch. FIG. 1A is a front view schematically showing the configuration of this type of arc welding robot, and FIG. 1B is a side view showing a portion around the welding torch of the arc welding robot as seen from the left side of FIG. 1A. As shown in FIG. 1A, in this arc welding robot, a welding torch 2 is attached to the distal end of an arm (or a forearm) of a robot mechanical section 1, and a wire feeding device 4 is mounted on a support base 5 of the robot arm (forearm). A torch cable 3 is laid between the wire feeding device 4 and the welding torch 2. In this connection, Japanese Unexamined Utility Model Publication (Kokai) No. 5-28563 (JP 5-28563 U) discloses an arc welding robot having the illustrated configuration.
It is required to supply, in addition to the welding wire, an assist gas and a welding current to the welding torch 2, and thus the torch cable 3 contains a plurality of umbilical members such as a gas pipe, an electric wire, etc. for feeding them. In general, the welding wire is fed to be passed through a tubular welding-wire liner, and the assist gas is supplied to flow in a tube. For supplying the welding current, several linear electrical conductors are used.
Thus, the torch cable 3 containing various umbilical members is subjected to a large load as the robot mechanical section 1 operates. For example, when a wrist axis of the robot mechanical section performs an orientation change (i.e., a turning) of the welding torch 2, the posture of the torch cable 3 changes to a large extent, as shown by broken lines 3a, 3b in FIG. 1B, due to the turning motion of the welding torch 2 (see broken lines 2a, 2b), so that the torch cable 3 is subjected to a bending or twisting action. In this connection, a cable structure (i.e., an umbilical-member managing structure) for reducing the load on the torch cable 3 has been proposed (see FIG. 2), as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2003-230963 (JP 2003-230963 A).
In the illustrated cable structure, a tubular liner (i.e., a conduit liner) 6 is disposed at the center of the torch cable 3, and the internal space of the liner 6 is used as a passage for a welding wire 7. The liner 6 is accommodated within a gas hose 8 for flowing an assist gas therethrough, and two or more (typically several) electrical conductors 9 are disposed on the outside of the gas hose 8. The electrical conductors 9 are arranged side-by-side along the outer circumference of the gas hose 8 so as to be spaced from each other, and a retainer tape 10 is wound around them from the outside thereof. Then, a sheath 11 is provided outside the retainer tape 10.
In the conventional cable structure as described above, the plural electrical conductors 9 are arranged to be spaced from each other, so that, when a deformation such as bending or twisting is generated in the torch cable 3, the electrical conductors 9 can individually move in a direction as to avoid the deformation such as bending or twisting. Therefore, the fatigue of the electrical conductors 9 due to deformation can be reduced.
A conventional torch cable has a structure, as does the cable structure as described above, in which a plurality of umbilical members, including a liner used for a welding wire, a tube for feeding an assist gas and plural electrical conductors for feeding a welding current, are contained together within a single cable having an outer diameter reduced to as small as possible, for the purpose of reducing a material cost and a radial dimension. As a result, the torch cable has a significantly low flexibility.
The low flexibility of the torch cable gives an unfavorable result in a case where it is used in an arc welding robot having a wire feeding device mounted on a forearm. As described above, in an arc welding robot, a welding torch moves freely as a wrist section operates, so that a torch cable is repeatedly subjected to bending or twisting. Therefore, if the torch cable with low flexibility is used, it is difficult to prevent premature cable breakage even when the torch cable has the cable structure as shown in FIG. 2. In particular, in a case where the torch cable is laid near the forearm or the wrist of the robot in order to avoid interference between the cable and a workpiece to be welded or a jig, a reduced length and a reduced radius of curvature are provided for a portion of the torch cable between the wire feeding device and the welding torch, so that a stress exerted upon the torch cable, due to bending or twisting, becomes large and this may shorten the life of the torch cable.